Electrophysiology is a specialty within the field of cardiology for the diagnosis and treatment of electrical abnormalities of the heart. Diagnosis is performed using electrode-bearing catheters placed within the heart chambers. Electrodes are positioned along the catheter shaft in a primarily two-dimensional array. Electrode elements are also spaced laterally around the catheter shaft give the array a limited third dimension which is limited because of the small catheter shaft diameter.
Cardiac electrical abnormalities are typically diagnosed by detecting the course of electrical activation paths along the endocardial surfaces of the heart chambers over time. Typically, several catheters are placed within one or more heart chambers to get a "picture" of the electrical activity. Sometimes, this electrical activity is cyclical, that is, it repeats fairly well from heartbeat to heartbeat. In such cases, one catheter can serve to perform the diagnosis by moving the electrodes to various regions and comparing point-by-point activation times with a reference. This reference can be an external electrocardiogram (EKG) or another electrode catheter maintained in a stable position within the heart chamber. However, certain types of electrical activity within a heart chamber are not cyclical. Examples include atrial flutter or atrial fibrillation, and ventricular tachycardia originating in scars in the walls of the ventricle that have resulted from infarcts. Such electrical activity is cyclical, that is, it is random from heartbeat to heartbeat. To analyze or "map" this type of electrical activity, the "picture" must be obtained during one heartbeat. In other words, all the points of the map or picture must be obtained simultaneously within one-tenth of a second.
One manner of treating these forms of acyclic electrical activities is by destroying the causative heart tissue through radio frequency (RF) catheter ablation. The procedure involves ablating accessory electrical pathways in the heart using an electrophysiology catheter. The catheter is guided through a vein or artery into the patient's heart and positioned at the site of the causative accessory pathway. The catheter transmits RF energy from an external source into the accessory pathway in an amount sufficient to destroy the tissue. The ablated tissue is replaced with scar tissue which interrupts the accessory pathway and restores the normal conduction of electrical activity in the heart.
Prior to ablation, the site of the accessory pathway must be ascertained using a diagnostic or mapping catheter typically composed of electrodes for stimulating and electrodes for sensing electrical activity. The procedure involves introducing a mapping catheter into the appropriate heart chamber where the arrhythmia condition exists. The heart tissue is stimulated in a manner intended to induce the arrhythmia and expose the abnormal electrical conduction. The resulting information enables an electrophysiologist to determine the appropriate course of treatment. The evaluation generally involves multiple tests to diagnose the arrhythmia and to assess the potential effectiveness of various treatment strategies. Once the heart tissue has been successfully mapped, the mapping catheter is removed and replaced with an ablation catheter at the treatment site. RF energy is then applied at the treatment site to ablate the accessory pathway.
An example of an electrophysiology catheter is shown in U.S. Pat. No. 4,365,639 to Goldreyer wherein is shown an electrode system for a cardiac pacemaker including a stimulating electrode at the distal end of the catheter and sensing electrodes on the catheter spaced away from the stimulating electrode. The sensing electrodes are circumferentially equidistant from the stimulating electrode. A problem with this catheter is that there is only one stimulating electrode at the distal end of the catheter for stimulating heart tissue ailment. Stimulating multiple areas in the heart requires a repositioning of the catheter.
Some electrophysiology catheters can function as both a mapping catheter and an ablation catheter. Typically, a catheter of this construction comprises a plurality of electrodes placed on the distal end of the catheter and a singular distal tip electrode. Some electrodes are used for mapping while the distal tip electrode is usually used for ablation. A drawback to this construction is that the electrophysiologist cannot use the distal tip electrode as a mapping electrode. Additionally, if the electrophysiologist uses the tip electrode as a mapping electrode, fine detailed mapping of the heart where the distal tip is in contact cannot occur because the tip is a singular electrode.
What is needed is a catheter having a plurality of electrodes at its distal end capable of stimulating and sensing cardiac electrical activity in multiple areas of the heart without requiring repositioning. What is also needed is an electrophysiology catheter able to maximize the efficacy of cardiac mapping by providing a plurality of electrodes at the distal end of the catheter for determining the direction of electrical activity. What is also needed is an electrode catheter for performing electrograms, pacing, stimulation and impedance measurement, preferably with the same catheter as for ablation and mapping.